1. Field of the Invention
The present invention relates to improving the image quality of a tomographic image of an eye.
2. Description of the Related Art
An eye tomographic imaging apparatus, such as an optical coherence tomography (OCT) apparatus, can be used for three-dimensional observation of a condition inside a retinal layer. Recently, tomographic imaging apparatuses have been drawing attention due to the fact that they are useful in providing more accurate diagnosis of diseases.
Ophthalmological diagnosis employs images such as a volume image for grasping a condition of an overall retinal layer, and a high-quality two-dimensional tomographic image for grasping layers that do not show up in a low-quality tomographic image.
The image quality of a tomographic image obtained by OCT depends on the intensity of the near infrared light incident on a retina. Therefore, to improve the image quality of a tomographic image, it is necessary to increase the intensity of the light irradiated on the retina. However, from a safety perspective, there is a limit to the intensity of the light that can be irradiated on the retina. Consequently, there is a need to generate a high-quality tomographic image while irradiating near infrared light in an intensity range that is not a problem in terms of safety. In response to this need, Japanese Patent Application Laid-Open No. 2008-237238 discusses a technique for generating a tomographic image with little noise by superimposing groups of captured two-dimensional tomographic images over each other.
On the other hand, if a thickness of each layer can be measured from a tomographic image of a retina imaged by OCT, a degree of progress of a disease such as glaucoma, or a post-treatment recovery outlook, can be quantitatively diagnosed. Japanese Patent Application Laid-Open No. 2007-325831 discusses a technique which, in order to quantitatively measure the thickness of these layers, detects a boundary of each layer in the retina from a tomographic image using a computer, and measures the thickness of each layer.
However, in Japanese Patent Application Laid-Open No. 2008-237238, one image is generated from images captured by different scanning lines. Consequently, there is a tradeoff between noise reduction and misregistration of an imaging position. Further, since eyes blink and subject to involuntary movement of fixation, adjacent images are not necessarily similar. Therefore, superimposing adjacent images does not always provide a doctor (hereinafter, sometimes referred to as “technician”) with a high quality image at the position which the doctor most wants to view. Moreover, when using a computer to detect the boundary of each layer in the retina from a tomographic image, and to measure the thickness of each layer, there is also a need to increase the accuracy of the layer detection in the tomographic images.